A. Field of the Invention
The present invention relates to devices and methods for sharpening or re-pointing twist drill bits. More particularly, the invention relates to an apparatus for automatically re-pointing twist drill bits.
B. Description of Background Art
Printed wiring boards (PWB's) used to hold and electrically interconnect electronic circuit components are typically fabricated as laminated stacks of copper foil sheets alternating with insulating sheets made of fiberglass, the latter containing glass fibers solidified with a resin such as epoxy. The glass fibers are highly abrasive, and can quickly dull drill bits used to drill holes in the PWB for receiving component leads, or for forming passageways or vias through the PWB. A typical PWB has a thickness of about 0.062 inch, and has hundreds of holes drilled through it. Each contact with the upper surface of a PWlB to drill a hole is referred to as a "hit." Since PWB's are usually arranged in stacks of two to five boards for drilling, a corresponding number of holes are drilled for each hit. Because the abrasive nature of the PWB board materials dulls typical drill bits after about 3000-5000 holes are drilled, the drill bit must be removed from service and re-sharpened after about 1,500-2,000 hits.
In conventional drill bit grinding apparatuses used to sharpen or re-point twist drill bits, the drill bit must be held in a chuck. Consequently, the operator must manually perform operations such as inserting the drill into the chuck of a drill bit holder mechanism, tightening the chuck to grip the drill, positioning or aligning the drill in relation to the drill bit holding mechanism and to a rotary grinding stone, advancing the drill bit towards a grindstone, retracting the re-pointed drill bit from the grindstone and removing the re-pointed drill bit. Because of all of the aforementioned operations, an operator can usually operate only a single drill bit grinding apparatus at a time. Thus, even an experienced operator can typically re-point no more than about 800 to 1,000 drill bits over an eight-hour work shift Therefore, there has been a strong demand for an automated drill bit re-pointing apparatus that has a higher throughput rate than existing re-pointing apparatuses, and which may be operated by less than highly skilled personnel. Despite a widespread need for an improved drill bit re-pointing apparatus, various difficulties have prevented the development of such an apparatus. The present invention was conceived of to provide an improved, automatic drill bit re-pointing apparatus in which functions performed manually in prior art devices are largely automated.